/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package it.ap.sa.core.configuration.commons;

import java.util.HashMap;

/**
 * <p>
 * A Configuration implementation that reads the platform specific environment
 * variables using the map returned by {@link System#getenv()}.
 * </p>
 *
 * <p>
 * This configuration implementation is read-only. It allows read access to the
 * defined OS environment variables, but their values cannot be changed. Any
 * attempts to add or remove a property will throw an
 * {@link UnsupportedOperationException}
 * </p>
 *
 * <p>
 * Usage of this class is easy: After an instance has been created the get
 * methods provided by the {@code Configuration} interface can be used for
 * querying environment variables, e.g.:
 * </p>
 *
 * <pre>
 * Configuration envConfig = new EnvironmentConfiguration();
 * System.out.println("JAVA_HOME=" + envConfig.getString("JAVA_HOME");
 * </pre>
 *
 * @author <a href="mailto:nicolas.deloof@gmail.com">Nicolas De Loof</a>
 * @version $Id: EnvironmentConfiguration.java 1210171 2011-12-04 18:32:07Z
 *          oheger $
 * @since 1.5
 */
public class EnvironmentConfiguration extends MapConfiguration {
	/**
	 * Create a Configuration based on the environment variables.
	 *
	 * @see System#getenv()
	 */
	public EnvironmentConfiguration() {
		super(new HashMap<String, Object>(System.getenv()));
	}

	/**
	 * Adds a property to this configuration. Because this configuration is
	 * read-only, this operation is not allowed and will cause an exception.
	 *
	 * @param key
	 *            the key of the property to be added
	 * @param value
	 *            the property value
	 */
	@Override
	protected void addPropertyDirect(String key, Object value) {
		throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
	}

	/**
	 * Removes a property from this configuration. Because this configuration is
	 * read-only, this operation is not allowed and will cause an exception.
	 *
	 * @param key
	 *            the key of the property to be removed
	 */
	@Override
	public void clearProperty(String key) {
		throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
	}

	/**
	 * Removes all properties from this configuration. Because this
	 * configuration is read-only, this operation is not allowed and will cause
	 * an exception.
	 */
	@Override
	public void clear() {
		throw new UnsupportedOperationException("EnvironmentConfiguration is read-only!");
	}
}
